The prevalence of childhood and adolescent obesity in the United States has approximately tripled over the last 30 years, with similar trends observed globally. This is a significant public health issue as children and adolescents who are obese are at greater risk for a spectrum of health problems in the near and long term. Substantial scientific effort has been devoted to understanding the causes of childhood obesity, and the overall obesity epidemic. Even with this significant endeavor there is an incomplete understanding of the etiology of obesity throughout the life-course. What can be concluded is that the causes of obesity are heterogeneous and likely result from a complex interplay between factors related to energy intake and expenditure, genetics, and environmental factors. Despite this incomplete understanding the vast majority of research has continued to focus on factors related to energy intake and expenditure and to a lesser extent genetics, socioeconomic and psychosocial aspects; the scientific community is acknowledging that research efforts need to be more comprehensive beyond these factors One burgeoning area of obesity related research has examined an infectious contributor, specifically human adenovirus-36 (Adv36). Animal studies have consistently shown that infection with Adv36 leads to excess adipose tissue deposition and obesity, while cellular and molecular studies have provided plausible underlying mechanisms. The studies in humans are limited to date. A handful of cross-sectional studies in adults have examined whether seropositivity for Adv36 infection is associated with obesity. Some showed a significantly greater proportion of Adv36 seropositivity in obese vs. non-obese participants, whereas others found no difference in prevalence of infection. On the other hand, the few cross-sectional studies that have examined this question in children all found a greater prevalence of Adv36 seropositivity in obese vs. non- obese children. These human studies are intriguing but limited by the lack of temporality, small samples, and simple statistical approaches. Therefore, we are proposing a more thorough study. Specifically, in 839 black and white girls from the NHLBI National Growth and Health Study (NGHS) we will assess the seropositivity of Adv36 at two time points using the gold standard assay. We will integrate this new measure into the rich database from the study and carry out comprehensive statistical analyses examining aspects of Adv36 infection with measures of childhood obesity.